External electrode fluorescent lamp, back light unit using the external electrode fluorescent lamp, LCD back light equipment using the back light unit and driving device thereof

ABSTRACT

The present invention relates to an external electrode fluorescent lamp which can provide higher degree of and more improved uniformity of brightness than those of conventional ones, and to a LCD back light unit using the external electrode fluorescent lamp. The present invention also relates to an equipment and a driving device to adapt the LCD back light unit. The external electrode fluorescent lamp of the present invention is comprising: an upper panel of lamp which is serpentine shaped; a lower panel which is planar shaped and to be combined with the upper panel to make channels between the upper panel and the low panel; and external electrodes which are located at the two extreme sides at the surface of the upper panel.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an external electrodefluorescent lamp, a liquid crystal display backlight unit using thesame, and a device for driving the external electrode fluorescent lamp,and more particularly to a liquid crystal display backlight unit usingan external electrode fluorescent lamp, which can easily produce asurface light source with higher brightness and brightness uniformitythan a conventional edge-type or a direct-type backlight unit, reduce acalorific value of a liquid crystal display panel due to electrodes of afluorescent lamp, prevent breakdown of a fluorescent lamp caused bybreakdown of electrodes, and extend the life of a fluorescent lamp, andfurther particularly, to an external electrode fluorescent lamp, liquidcrystal display backlight unit using the same and device for driving anexternal electrode surface emission fluorescent lamp, which can simplifythe manufacturing process and improve the productivity thereof, andwhich can be easily applied to a large-scale backlight unit.

2. Description of Related Art

Generally, a liquid crystal display (LCD) used as display means forcharacters, graphics and moving pictures has been greatly highlighted asa next generation display device for mobile phones or televisionsbecause it causes less fatigue of eyes than a conventional cathode raytube (CRT) display device, and it can realize miniaturization, lightweight, and low power consumption.

The construction of a conventional LCD panel in which characters orimages are displayed on LCD is described in brief. First, if liquidcrystal material is injected between a pair of surface-processedtransparent glass plates, and an electrical signal (voltage) is suppliedto the injected liquid crystal material using an LCD driving circuit(not shown) for generating a driving signal, phase variation of theliquid crystal material occurs by the electrical signal. The LCD drivingcircuit applies different voltages to the liquid crystal material tovary distribution of the liquid crystal material, thus enabling specificcharacters or images to be displayed.

However, since an LCD panel on which characters are displayed cannotemit light for itself, a means for assisting in visually recognizingcontents (characters or logos) displayed on the panel is required.Currently, a backlight system using lamps which irradiate light from thesides or the back of a LCD panel is generally used as the assistingmeans.

Conventional backlight systems are mainly classified into edge-typebacklight units and direct-type backlight units according to positionsof fluorescent lamps projecting light. The edge-type backlight unitsemploy a manner in which light sources are positioned beneath both sidesof the panel, such that light inputted from the light sources forms asurface light source by a light guide plate and a reflective sheet andthe surface light source illuminates cells of the LCD panel. Such anedge-type backlight unit is advantageous in that, since it indirectlyguides light radiated from the light sources, brightness uniformity ishigh. However, it is problematic in that brightness decreases relativeto the brightness uniformity.

FIG. 1 shows an embodiment of a conventional edge-type backlight unit.Referring to FIG. 1, a lamp cover for covering fluorescent lamps, thefluorescent lamps for radiating light by the supply of power, areflective sheet for reflecting the radiated light in a predetermineddirection, a light guide plate for guiding the radiated light, adiffusion sheet for uniformly radiating incident light to prisms, avertical prism, a horizontal prism, and a protective sheet are layeredin order from the bottom. In the above-described edge-type backlightunit, since the fluorescent lamps are positioned at the side of thelight guide plate, brightness uniformity increases, while brightnessdecreases.

Further, the direct-type backlight units employ a manner in which lightsources (cold cathode fluorescent lamps) are arranged beneath an LCDpanel, a diffusion sheet is arranged on the front of the light sources,and a reflective sheet is arranged on the back of the light sources,such that light radiated from the light sources is reflected anddiffused to be irradiated onto cells of the LCD panel. Since such adirect-type backlight unit effectively uses light using the reflectivesheet and the diffusion sheet, it can obtain high brightness, so it issuitable for backlight units requiring high brightness. However, thedirect-type backlight unit is problematic in that it cannot providesufficient brightness according to the size of LCD panels which becomelarge, and brightness uniformity is also decreased.

Moreover, the conventional direct-type backlight unit requires as manyinverters as the number of fluorescent lamps used as light sources. Thatis, characteristics of respective fluorescent lamps used as the lightsources are slightly different. Therefore, in the case where thefluorescent lamps are connected in parallel with each other, thereoccurs a problem that a plurality of fluorescent lamps are notsimultaneously turned on due to the difference in discharge properties,if one inverter having a high power supplying capability is mainly used.That is, some of fluorescent lamps may be turned on, and the remainingfluorescent lamps may be turned on late or turned off. In order to solvethe problem, inverters are respectively connected to fluorescent lampsto drive the fluorescent lamps. However, there are problems, such ashigh power consumption, cost increase due to the increased number ofinverters, and productivity decrease due to the increased assembly time,degradation of LCD due to heat generated by electrodes, etc.

Further, a prior art, plate-type surface emission fluorescent lampapplied by the present applicant, improves brightness uniformity andbrightness of conventional light sources (fluorescent lamps) forbacklighting. FIG. 12 is a plan view of a previously applied surfaceemission fluorescent lamp. As shown in FIG. 12, an upper sheet of thelamp is constructed such that serpentine-shaped channels into whichdischarge gas is injected and which are isolated from the outside arearranged to be adjacent to each other. Further, bent portions aremutually connected, such that a single channel is formed in the uppersheet. At both ends of the single channel, internal electrodes 201 areinstalled.

FIG. 13 is a sectional view by A—A line of the surface emissionfluorescent lamp 203 of FIG. 12, and shows sections of channels 203 aformed adjacent to each other. Actually, the channels 203 a shown to beseparated respectively are mutually connected to each other to form asingle path. In FIG. 13, although the section “A” is depicted by asemicircle, the shape of the channels 203 can be varied to a rectangle,a diamond, etc.

Further, FIG. 14 is a sectional view by B—B line of FIG. 12, and showsthe installation of the internal electrodes 201 of the surface emissionfluorescent lamp 203. As shown in FIG. 14, one end of each of theinternal electrodes 201 is inserted into the surface emissionfluorescent lamp 203. Therefore, many manufacturing processes are addedto insert and fix the internal electrodes 201.

As described above, the previously applied surface emission fluorescentlamp 203 uniformly radiates light over the entire surface area, thussupplementing the disadvantages of the conventional edge-type anddirect-type backlight units to provide high brightness and highbrightness uniformity. Especially, since the surface emissionfluorescent lamp 203 has serpentine-shaped channels, the brightness andthe brightness uniformity are remarkably improved. Further, the shape ofthe surface emission fluorescent lamp 203 can be changed to “L”, “W”,etc. In this case, the upper sheet of the lamp is typically formed inthe shape of “L” or “W”, and the lower sheet thereof is formed in theshape of a plate, such that the upper and lower sheets are manufacturedto be combined with each other, or to be integrated.

However, as the construction of the fluorescent lamp is varied asdescribed above, there are inconveniences in that installation positionsof the internal electrodes 201 for supplying power to the fluorescentlamp are frequently varied, so manufacturing equipment must be changed.Moreover, the internal electrodes 201 are fixedly inserted into thesurface emission fluorescent lamp 203, thus causing several problems,such as increase of the manufacturing process of the fluorescent lampand the deterioration of productivity due to breakdown of internalelectrodes, etc. Further, the surface emission fluorescent lamp isproblematic in that, if a plurality of fluorescent lamps are connectedin parallel to apply the fluorescent lamps to a large-scale backlightunit, wiring is complicated to connect inverters to respectiveelectrodes, so the volume of the backlight unit increases.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind theabove problems occurring in the prior art. The present invention is anLCD backlight unit using an external electrode fluorescent lamp, whichcan easily produce surface light sources, reduce a calorific value of anLCD panel caused by electrodes, prevent breakdown of the externalelectrode fluorescent lamp due to the breakdown of electrodes, andextend the life of the external electrode fluorescent lamp.

The present invention is also an LCD backlight unit using an externalelectrode fluorescent lamp, which can simplify the manufacture of abacklight unit, and improve driving characteristics of a fluorescentlamp by changing a power supplying manner for a fluorescent lamp used ina conventional direct-type backlight unit.

The present invention is also an LCD backlight unit using an externalelectrode fluorescent lamp, in which a backlight unit is produced as amodule, thus greatly reducing time required for assembly, andconsequently improving productivity.

The present invention is also an external electrode surface emissionfluorescent lamp for LCDs and backlight unit using the same, in whichelectrodes of a surface emission fluorescent lamp used for LCDbacklighting are constructed as external electrodes, thus simplifyingthe manufacturing process of the surface emission fluorescent lamp,improving productivity, enabling a large-scale backlight unit to beeasily produced, and enabling produced LCD panels to be miniaturized andthinned.

The present invention is also an external electrode surface emissionfluorescent lamp for LCDs and backlight unit using the same, which has agetter housing for supplying mercury to the inside of channels of thesurface emission fluorescent lamp and absorbing several impurities.

The present invention is also a device for driving a surface emissionfluorescent lamp for LCDs, which applies an initial lighting voltage forgenerating charged particles to a surface emission fluorescent lamp forLCDs having main electrodes and auxiliary electrodes, and applies alighting maintaining voltage to the surface emission fluorescent lampbefore generated charged particles disappear, thus maintaining a litcondition of the surface emission fluorescent lamp.

The present invention is also a device for driving a surface emissionfluorescent lamp for LCDs, which can operate stably even at a lowvoltage and reduce continuous stress of a transformer and losses ofswitching devices due to a high voltage during initial lighting, andwhich controls a surface emission fluorescent lamp having mainelectrodes and auxiliary electrodes.

More specifically, the present invention is an LCD backlight unit forradiating light used to read characters displayed on an LCD panel frombelow, comprising an inverter for generating first and second voltagesusing a direct current (DC) voltage and supplying the first and secondvoltages through first and second output lines, respectively; aplurality of external electrode fluorescent lamps each having a firstend electrode connected to one of the first and second output lines forsupplying the first and second voltages received from the inverter, anda second end electrode arranged opposite to the first end electrode andconnected to the ground, the external electrode fluorescent lamps beingsequentially arranged on the same plane; and a base for accommodatingthe external electrode fluorescent lamps by allowing the sequentiallyarranged external electrode fluorescent lamps to be fixed.

Further, the present invention is an external electrode surface emissionfluorescent lamp for LCD backlighting, comprising a serpentine-shapedupper sheet having a section for maximizing brightness uniformity withina predetermined distance from its surface; a plate-shaped lower sheetcombined with the upper sheet to form mutually connected channels; andmain electrodes and auxiliary electrodes installed on surfaces of bothends of the upper sheet.

Further, the present invention is an external electrode surface emissionfluorescent lamp having the construction in which channels mutuallyadjacent to each other are isolated to prevent discharge gas frompassing through the channels, and a plurality of gas paths, whosethickness, installation position and number are variable, are installedbetween adjacent channels.

Further, the present invention is a device for driving an externalelectrode surface emission fluorescent lamp for LCDs having mainelectrodes and auxiliary electrodes, the driving device supplying powerto the external electrode surface emission fluorescent lamp, comprisinga main controller for lighting the surface emission fluorescent lamp inresponse to a control signal from an LCD controller, a priming circuitfor supplying power to the auxiliary electrodes for a predeterminedperiod of time so as to generate initial charged particles in theexternal electrode surface emission fluorescent lamp in response to thecontrol signal from the main controller; and a lighting maintainingcircuit for supplying power to the main electrodes so as to apply alighting maintaining voltage using the charged particles generated bythe priming circuit.

Lastly, the present invention is a driving device further comprising afeedback circuit for detecting a current flowing into the surfaceemission fluorescent lamp, converting the current into a voltage andoutputting the voltage to the main controller, thus enabling an inputvoltage for brightness control to be controlled through the lightingmaintaining circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a conventional edge-type backlight unit;

FIG. 2 is a view showing the wiring of a backlight unit according to thepresent invention;

FIG. 3 is a perspective view of a base unit according to the presentinvention;

FIGS. 4 to 6 are side views of a fluorescent lamp into which electrodesand rubber holders are inserted;

FIGS. 7 and 8 are views showing the connection of output lines forsupplying power to the fluorescent lamp;

FIG. 9 is a block diagram of an inverter for supplying power to thefluorescent lamp;

FIG. 10 is a detailed circuit diagram of the inverter of FIG. 9;

FIG. 11 is a waveform diagram showing driving pulses used by theinverter;

FIG. 12 is a plan view of a conventional surface emission fluorescentlamp;

FIG. 13 is a sectional view by A—A line of FIG. 12;

FIG. 14 is a sectional view by B—B line of FIG. 12;

FIG. 15 is a plan view of an external electrode surface emissionfluorescent lamp according to a preferred embodiment of the presentinvention;

FIG. 16 is a plan view of another external electrode surface emissionfluorescent lamp according to another preferred embodiment of thepresent invention;

FIG. 17 is a view showing the installation of auxiliary electrodes ofthe external electrode fluorescent lamp of the present invention;

FIG. 18 is a view showing another installation of auxiliary electrodesof the external electrode fluorescent lamp of the present invention;

FIG. 19 is a sectional perspective view of a part “B” of FIG. 15 forshowing the installation of a getter;

FIG. 20 is a sectional perspective view showing another installation ofthe getter;

FIG. 21 is a side sectional view of a backlight unit according to thepresent invention;

FIG. 22 is a plan view of a conventional surface emission fluorescentlamp having external electrodes;

FIG. 23 is a block diagram of a device for driving a fluorescent lampaccording to a preferred embodiment of the present invention;

FIG. 24 is a block diagram of another device for driving a fluorescentlamp according to another preferred embodiment of the present invention;

FIG. 25 is a detailed circuit diagram of the fluorescent lamp drivingdevice of FIG. 23;

FIG. 26 is a detailed circuit diagram of the fluorescent lamp drivingdevice of FIG. 24; and

FIG. 27 is a flowchart showing the operation of a device for driving asurface emission fluorescent lamp of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 is a view showing the wiring of a backlight unit according to thepresent invention. The backlight unit of the present invention comprisesan inverter 90 and a base 100. The inverter 90, which is used to supplylighting voltages to a plurality of external electrode fluorescentlamps, 110, generates first and second voltages and supplies the firstand second voltages to the external electrode fluorescent lamps 110through first and second output lines 120 and 122. The base 100 includesthe plurality of fluorescent lamps 110 lit by receiving the first andsecond voltages from the inverter 90.

The fluorescent lamps 10 are external electrode fluorescent lamps havingexternal electrodes, not internal electrodes formed at both ends of afluorescent lamp like a conventional fluorescent lamp. Even though theexternal electrodes are not indicated by a specific reference numeral inFIG. 2, they are formed to be protruded from both ends of each of thefluorescent lamps 110, wherein, a contact point 118 is formed on any oneof the both-end external electrodes of each of the fluorescent lamps110.

The external electrode fluorescent lamps 110 are divided into two partsby odd and even orders, such that they are supplied with lightingvoltages through the first output line 120 or the second output line 122connected to the inverter 90. Referring to FIG. 2, the voltages suppliedto the fluorescent lamps 110 are supplied through the contact points 118connected to the first or second output line 120 or 122 every otherlamp. The contact points 118 are electrically connected to theelectrodes formed on end portions of the fluorescent lamps 110 bysoldering, which will be described later. Therefore, the fluorescentlamps 110 on which the contact points 118 coming into contact with theoutput lines are formed are supplied with power through correspondingoutput lines.

In this way, stable supply of power can be achieved by supplyingvoltages using the first and second output lines. An electrode 112 ofthe other end of each of the fluorescent lamps 110, which is notsupplied with power, is connected to the ground. Connection manners forthe first and second output lines 120 and 122, which can be consideredas another characteristics of the present invention, will be describedlater.

Referring to FIG. 3, the base 100 for accommodating the externalelectrode fluorescent lamps 110 is formed in the shape of an openrectangular box in which a pair of isolation plates 102 longitudinallyextended and arranged opposite to each other, and a pair of lamp fixingplates 104 having both ends connected to the isolation plates 102 andbeing opposite to each other, are constructed to form four sides of arectangle, and a reflective sheet 106 is further installed on thebottom.

Even though not shown in FIG. 3, after the external electrodefluorescent lamps 110 are horizontally arranged, a diffusion sheet isarranged over the fluorescent lamps 110, thus enabling the base 100 tobe produced in the form of a full rectangular box. Further, terminalsfor connecting the first and second output lines 120 and 122 are formedon the side of the base 100. In this way, if the base 100 is produced asa box-shaped module, the assembly of the backlight unit can be promptlyaccomplished.

On the pair of lamp fixing plates 104, a plurality of lamp fixing holes108 are oppositely formed at regular intervals. The lamp fixing holes108 are used to fix the external electrode fluorescent lamps 110 in aline. The lamp fixing holes 108 allow the external electrode fluorescentlamps 110 to be fixed thereto using rubber holders.

The reflective sheet 106 reflects light radiated from the externalelectrode fluorescent lamps 110 arranged thereon. A reflective sheetwith a coating-processed surface and with high reflection efficiency canbe used as the reflective sheet 106.

FIGS. 4 and 5 show the electrodes 112 formed on circumferences of bothends of the external electrode fluorescent lamp 110. The electrodes 112serve to supply a high voltage to the fluorescent lamp 110 so as tosufficiently excite the fluorescent lamp 110 when high voltage pulsesare applied to the fluorescent lamp 110 from the outside. The electrodes112 are produced using materials with excellent conductivity, forexample, copper, aluminum tape, etc.

Further, the electrodes can be formed such that they fully enclose thecircumferences of both ends of the external electrode fluorescent lamp110, as shown in the electrodes 112 of FIG. 4, or they partially encloseupper portions or lower portions of circumferences of both ends thereof,as shown in electrodes 114 of FIG. 5. The advantage of the former is inthat, since the areas of the electrodes 112 are wide, sufficientexciting power can be provided to sufficiently light the externalelectrode fluorescent lamp 110 when high voltage pulses are applied. Onthe other hand, the latter has an advantage in that, since electrodes114 partially cover the surface of the external electrode fluorescentlamp 110, a large amount of light is radiated, thus improving lightradiating efficiency of fluorescent lamps.

In left sides of FIGS. 4 and 5, side views of the external, electrodefluorescent lamp 110 are simply depicted. Referring to FIG. 4, it can beseen that the electrodes 112 are formed to fully enclose circumferencesof both ends of the external electrode fluorescent lamp 110. Further,referring to FIG. 5, it can be seen that the electrodes 114 arepartially formed on only lower circumferences (or upper circumferences)of both ends of the external electrode fluorescent lamp 110.Applications of the electrodes 112 and 114 will be described later.

FIG. 6 shows the coupling of rubber holders 116 for allowing theexternal electrode fluorescent lamps 110 to be fixed to the lamp fixingholes 108 formed in the base 100. The rubber holders 116 are interlockedwith both ends of the external electrode fluorescent lamp 110, and areeach comprised of two parts having different diameters. In a first parthaving a smaller diameter, a hole for accommodating an end of theexternal electrode fluorescent lamp 110 is formed. A second part havinga larger diameter is adhered closely and fixed to the border surface ofeach of the lamp fixing holes 108. A left side of FIG. 6 shows a sideview of the rubber holder 116. As described above, the present inventionis advantageous in that it employs the external electrode fluorescentlamps 110, thus enabling the fluorescent lamps to be easily installed.

FIGS. 7 and 8 are views respectively showing the connections of thefirst and second output lines 120 and 122 for supplying, power to theexternal electrode fluorescent lamps 110.

FIG. 7 shows the positions of the contact points 118 and the wiring (offirst and second output lines) if each of the electrodes 112 circularlyencloses the circumference of the external electrode fluorescent lamp110. Both the first and second output lines 120 and 122 are coated withcovering material, so they are insulated. Therefore, only parts cominginto contact with the contact points 118 are exposed to transmitelectricity.

The first output line 120 passes over an external electrode fluorescentlamp 110 a which is located first from the left side, and is connectedwith the electrode 112 through the contact point 118. After beingconnected with the electrode 112, the first output line 120 passes underan external electrode fluorescent lamp 110 b, which is located secondfrom the left side, without any electrical connection. Further, thefirst output line 120 is connected with the contact point 118 on anexternal electrode fluorescent lamp 110 c, which is located third fromthe left side. That is, it can be seen that the first output line 120 iselectrically alternately connected to external electrode fluorescentlamps 110 a, 110 c and 110 e which are positioned in odd order. Thecontact points 118 are electrically connected to both the first andsecond output lines 120 and 122 by soldering.

Contact points can be directly formed by soldering or can be formed inthe shape of a ring on the surface of the electrode. That is,ring-shaped contact points are formed, the first output line (or thesecond output line) is inserted into the contact points, and the contactpoints are then electrically connected to the first or second outputline by soldering, thus simplifying the assembly of the backlight unit.

On the other hand, the second output line 122 passes under the firstexternal electrode fluorescent lamp 110 a (in the opposite direction ofthe first output line 120), and is connected to the contact point 118 onthe second external electrode fluorescent lamp 110 b. The second outputline 122 connected to the contact point 118 passes under the thirdexternal electrode fluorescent lamp 110 c and extended to the top of thenext fluorescent lamp. That is, it can be seen that the second outputline 122 is alternately connected to the external electrode fluorescentlamps 110 b, 110 d and 110 f, which are positioned in even order.Therefore, if power is supplied to both the first and second outputlines 120 and 122, the first output line 120 supplies power to theexternal electrode fluorescent lamps 110 a, 110 c, and 110 e), and thesecond output line 122 supplies power to the external electrodefluorescent lamps 110 b, 110 d and 110 f.

Further, the external electrode fluorescent lamps 110 a to 110 f arewired to the first and second output lines 120 and 122 while beingenclosed by the first and second output lines 120 and 122. Especially,it is preferable to adhere the first and second output lines 120 and 122to the surfaces of the fluorescent lamps, through which the output lines120 and 122 pass, as closely as possible. Due to this wiringconstruction, a sufficient electric field is generated when high voltagepulses are applied from the inverter 90. Due to the sufficient electricfield, lighting operations of external electrode fluorescent lamps canbe indirectly improved.

FIG. 8 shows the wiring mariner fundamentally similar to that of FIG. 7,wherein the wiring manner of FIG. 8 is different from that of FIG. 7 inpositions where contact points 118 of the first and second output lines120 and 122 are formed. In this case, the contact points 118 are alwaysformed on the lower surfaces of electrodes. In FIG. 8, even though thecontact points 118 are different from those of FIG. 7, it is clear thatthe contact points 118 can be applied to any of circular electrodes orpartially formed electrodes.

Further, the wiring of the first and second output lines 120 and 122 isachieved such that the output lines 120 and 122 are adhered closely tothe external electrode fluorescent lamps to enclose them, as shown inFIG. 8. Therefore, a sufficient electric field is generated when highvoltage pulses are applied from the inverter. Due to the sufficientelectric field, lighting operations of external electrode fluorescentlamps can be indirectly improved.

Further, in the wiring of the output lines of the present invention, thepositions of the contact points 118 are not limited by embodiments shownin the drawings. On the other hand, it is clear that the contact pointsare formed and soldered at convenient positions to connect the externalelectrode fluorescent lamps with the first and second output lines 120and 122.

A block diagram of the inverter 90 for supplying power to the pluralexternal electrode fluorescent lamps 110 having the above constructionis depicted in FIG. 9, and a detailed circuit diagram of the inverter 90of FIG. 9 is depicted in FIG. 10. The inverter 90 is described in detailwith reference to FIGS. 9 and 10.

The inverter 90 comprises a line filter 10, a pulse generator 20, a pairof driving buffers 30 and 30′, a pair of resonance circuits 40 and 40′,a pair of step-up transformers 50 and 50′, and a feedback circuit 70.The line filter 10 rectifies a direct current (DC) voltage supplied by aDC power unit, and outputs the rectified DC voltage. The pulse generator20 generates switching driving pulses. The driving buffers 30 and 30′selectively output driving pulses generated by the pulse generator 20 tothe resonance circuits 40 and 40′. The resonance circuits 40 and 40′,which are driven by the driving pulses outputted from the drivingbuffers 30 and 30′, convert the DC voltage received from the line filter10 into an alternating current (AC) voltage and output the AC voltage.The step-up transformers 50 and 50′ amplify each of the AC voltagesoutputted from the resonance circuits 40 and 40′, respectively, andoutput the amplified AC voltage to the external electrode fluorescentlamps 110 which are divided into two groups. The feedback circuit 70detects a secondary voltage used to control brightness of the externalelectrode fluorescent lamps 110. High voltages outputted from thetransformers 50 and 50′ of the inverter 90 are synchronized and operatedat the same phase and same frequency, thus enabling the externalelectrode fluorescent lamps 110 to be synchronously driven. By thesynchronous driving of the two transformers, the fluorescent lamps 110of the present invention can obtain more stable and improved operationcharacteristics compared with a case where a single transformer is used.

The operations of the inverter 90 are described in detail.

The line filter 10 receives DC power from the DC power unit (rectifyingunit, battery or rechargeable battery), and rectifies the DC power tosupply a stable current. Referring to FIG. 10, the line filter 10consists of a coil L11 and a condenser C11, and serves to rectify andoutput a DC voltage supplied by the DC power unit. The DC voltageoutputted from the line filter 10 is inputted to a center tap of each ofthe step-up transformers 50 and 50′. However, the DC voltage iscontrolled by the resonance circuits 40 and 40′ to be modulated andoutputted as an AC voltage.

The pulse generator 20, which is used to generate switching drivingpulses, transmit the driving pulses to the driving buffers 30 and 30′,respectively. Further, the pulse generator 20 controls voltage valuessupplied to the fluorescent lamps by varying the widths of the generatedpulses in response to a signal received from the feedback circuit 70.The pulse generator 20 supplies a DC voltage for performing a stableoperation using a regulator. Referring to FIG. 10 the pulse generator 20outputs two pulse signals.

The driving buffers 30 and 30′ output the driving pulses generated bythe pulse generator 20 to the resonance circuits 40 and 40′. As shown inFIG. 10, the driving buffers 30 and 30′ are comprised of NPN transistorsQ1 and Q3 and PNP transistors Q2 and Q4, and NPN transistors Q5 and Q7and PNP transistors Q6 and Q8, respectively. One pulse outputted fromthe pulse generator 20 is inputted to a base of each of the transistorsQ1 and Q2 of the driving buffer 30. The other pulse outputted from thepulse generator 20 is inputted to a base of each of the transistors Q3and Q4. These operations are applied to the driving buffer 30′ in thesame manner as the driving buffer 30. Therefore, driving points arevaried according to waveform of pulses outputted from the pulsegenerator 20.

The resonance circuits 40 and 40′ each convert the DC voltage receivedfrom the line filter 10 into a voltage signal of a predeterminedfrequency and output the voltage signal, in response to the switchingpulse signals outputted from the driving buffers 30 and 30′. By theswitching driving pulses of the pulse generator 20 and operations of theresonance circuits 40 and 40′, AC voltage pulses of predeterminedfrequency are generated.

The outputted AC voltages are inputted to the step-up transformers 50and 50′, respectively, and sufficiently boosted. The boosted voltagesare supplied to the external electrode fluorescent lamps 110. Thevoltages supplied to the external electrode fluorescent lamps 110 arehigh voltage signals having the, same frequencies and the same phases,as described above, and are used to drive the external electrodefluorescent lamps 110. The voltages outputted from the step-uptransformers 50 and 50′ are respectively supplied to the externalelectrode fluorescent lamps 110 through the first and second outputlines 120 and 122 shown in FIG. 2. Since the output voltages have thesame phases and frequencies, there is no difficulty in operating thefluorescent lamps 110 even though any one of the output lines 120 and122 is connected to each of the two voltages.

The feedback circuit 70 detects a current flowing into the externalelectrode fluorescent lamps 110 in a secondary side as a voltage using aresistor R71, and outputs a control signal so as to vary brightness ofthe external electrode fluorescent lamps 110 on the basis of thevoltage. The widths of the driving pulses generated by the pulsegenerator 20 are varied due to the signal received from the feedbackcircuit 70, thus optimizing the brightness of the external electrodefluorescent lamps 110.

FIG. 11 is a waveform diagram showing the driving pulse signals of theinverter 90 of the present invention, and shows the pulse signals ch1and ch2 generated by the pulse generator 20. As shown in FIG. 11, thedriving pulse signals inputted to the driving buffers 30 and 30′ havethe same frequencies in different phases. The resonance circuits 40 and40′ are operated by the driving pulse signals to generate AC voltages.

An external electrode surface emission fluorescent lamp capable ofsubstituting for the above-described bar-shaped external electrodefluorescent lamp and a backlight unit using the same are describedlater. The construction of such an external electrode surface emissionfluorescent lamp is an improved structure of the surface emissionfluorescent lamp previously applied by the present applicant. Due tothis structure, a plurality of bar-shaped fluorescent lamps can bereplaced with a single external electrode surface-emission fluorescentlamp.

That is, if an LCD panel is constructed as a large-scale panel, theexternal electrode surface emission fluorescent lamp as described latercan be substituted for the bar-shaped external electrode fluorescentlamps, so a display area can be increased.

FIG. 15 is a plan view of the above-described surface emission externalelectrode fluorescent lamp 203. As shown in FIG. 15, it can be seen thatbar-shaped external electrodes 202 are formed at both ends of thesurface emission fluorescent lamp 203 which is serpentine-shaped and isconstructed as a single channel. The external electrodes 202 are simplyimplemented by attaching conduction materials for enabling electricityto easily pass therethrough to both ends of the lamp 203. Especially,since energy must be provided to the inside of the external electrodesurface emission fluorescent lamp 203 through external surfaces of theelectrodes 202, the electrodes 202 have sufficiently wide surface areasso as to provide sufficient excitation energy.

The external electrodes 202 serve to supply a high voltage to thesurface emission fluorescent lamp 203 so as to sufficiently excite thesurface emission fluorescent lamp 203 when high voltage pulses areapplied to the fluorescent lamp 203 from the outside. The externalelectrodes 202 are produced using materials with excellent conductivity,for example, copper, aluminum tape, etc. In this case, the conductionmaterials are not inserted into the surface emission fluorescent lamp203 like the internal electrodes 201 of FIG. 14, but brought intocontact with the surface of the fluorescent lamp 203 and fixed not to beseparated from the fluorescent lamp 203 during the operation of thefluorescent lamp 203, thus completing the attachment of the materials.

FIG. 16 shows a modified embodiment in which gas paths 207 are formedbetween adjacent channels 203 b of the external electrode surfaceemission fluorescent lamp 203 of the present invention. This embodimentshows that mutual horizontal channels are connected through the gaspaths 207, compared with the embodiment of FIG. 15 in which respectivebent portions of the external electrode surface emission fluorescentlamp 203 are connected to each other to form a single channel. Such aconstruction is advantageous in that it can uniformly distributedischarge gas into the surface emission fluorescent lamp 203 at avelocity higher than a moving velocity of discharge gas in the singlechannel construction shown in FIG. 12. Although it is depicted in FIG.16 that one gas path 207 is formed in both ends of each of horizontalchannels, the thickness, installation position and the number of the gaspaths 207 can be varied. Obviously, it is clear that these modificationsor variations are included in the scope of the present invention. Adistribution speed of gas can be optimized by varying the thickness,installation position and the number of the gas paths 207 according tothe length or thickness of the surface emission fluorescent lamp 203.

FIGS. 17 and 18 show the installation of auxiliary electrodes fordriving the external electrode fluorescent lamp of the present inventionat a low voltage. The external electrode surface emission fluorescentlamp 203 is long, so a high voltage is required to discharge it.Therefore, it is preferable to employ the auxiliary electrodes.

That is, if a voltage is applied to auxiliary electrodes connected toadditional power, charged particles are generated within the fluorescentlamp 203. Thereafter, if a voltage is applied to the external electrodes202 used as main electrodes, the surface emission fluorescent lamp 203starts discharging even at a low voltage. Therefore, if the auxiliaryelectrodes are used, power consumption can be greatly reduced comparedwith an external electrode surface emission fluorescent lamp using onlymain electrodes. The auxiliary electrodes are installed on the surfaceof the surface emission fluorescent lamp 203 in the same manner as thatof the external electrodes 202. In this case, the auxiliary electrodescan be installed in the shape of a line, without occupying a wide area.

FIG. 17 shows that auxiliary electrodes 202 a are formed to enclose eachof the channels 203 b. On the other hand, FIG. 18 shows that auxiliaryelectrodes 202 b are formed to pass along both ends of each of channels203 b. The installation position of the auxiliary electrodes can bevaried in consideration of the length, area, etc. of the externalelectrode surface emission fluorescent lamp 203. That is, if it isrequired to shorten a response time of the surface emission fluorescentlamp 203, auxiliary electrodes are installed on the same positions asthose of the auxiliary electrodes 202 a of FIG. 17, while if it ispermitted to delay a response time to some degree, they are installed onthe same positions as those of the auxiliary electrodes 202 b of FIG.18. In this case, it is preferable that the auxiliary electrodes use adifferent power source from that of the external electrodes.

Further, in the surface emission fluorescent lamp 203 of the presentinvention, an upper sheet 205 and a lower sheet 206 can be manufacturedto be integrated, or separately manufactured and fused later. The formercase is disadvantageous in that it is difficult to apply fluorescentmaterials; while it is advantageous in that it simplifies amanufacturing process because it does not execute a sealing process. Onthe contrary, the latter case is disadvantageous in that it requires asealing process for junction portions, while it is advantageous in thatthe application of fluorescent materials can be easily performed.

The surface emission fluorescent lamp 203 further has a getter insertedthereinto. The getter 208 is used to supply mercury into the channels203 b of the surface emission fluorescent lamp 203 and absorb severalimpurities existing in the channels 203 b. The getter 208 is fixed by agetter housing such that it cannot move in the channels 203 b.

FIGS. 19 and 20 shows embodiments of the getter housing 209. Theembodiment of FIG. 19 can be applied to a case where the getter housing209 is installed in a bent portion, that is, a bent portion B′ of eachof channels indicated in FIG. 15. The getter housing 209 of FIG. 19 hasa portion exposed to the outside in the shape of a quarter of a circle,and has a center portion dented inwardly on the inner surface of thegetter housing 209 to fix the getter 208. Further, the getter housing209 can be constructed such that dented portions are formed on both theinner and outer surfaces of the getter housing 209.

On the other hand, FIG. 20 shows that a getter housing is formed in aportion of a bar-shaped channel, in which both ends of a channel areinwardly dented. It is clear that the fixing position of the getter 208can be formed in any places within a range without preventing lightradiation of the surface emission fluorescent lamp 203.

An embodiment of a backlight unit using the surface emission fluorescentlamp 203 of the present invention having the above construction is shownin FIG. 21.

As shown in FIG. 21, a diffusion sheet 212 is arranged on the upperportion of the backlight unit, a reflective sheet 214 is arranged on thelower portion thereof, and the surface emission fluorescent lamp 203 isinserted therebetween. Even though not shown in detail, the diffusionsheet 212, the reflective sheet 214 and the surface emission fluorescentlamp 203 are fixed to a frame of the backlight unit. External electrodes202 are also attached to the surface emission fluorescent lamp 203, asshown in FIG. 17, such that power is supplied from the outside.

Numerical values indicated in the left side of FIG. 21 are values of anoptimized manufacturing embodiment of a backlight unit having a sizeequal to or greater than 15.1″ and having brightness uniformity of 90%.The thickness of the diffusion sheet 212 is 2 mm, the thickness of thesurface emission fluorescent lamp 203 is 7.1 mm, the thickness of thereflective sheet 214 is 1 mm, a spaced distance between the diffusionsheet 212 and the surface emission fluorescent lamp 203 is 1.9 mm, and aspaced distance between the reflective sheet 214 and the surfaceemission fluorescent lamp 203 is 0.1 mm, so the backlight unit isproduced to have an entire thickness of 12.1 mm. These numerical valuesare values optimized under the above conditions satisfying the sizeequal to or greater than 15.1″ and the brightness uniformity equal to orgreater than 90%. Further, a predetermined voltage is applied to theexternal electrodes 202 of the surface emission fluorescent lamp 203using a power supply circuit (not shown), thus operating the backlightunit.

In the above backlight unit, even though only the external electrodes202 are attached to the external electrode surface emission fluorescentlamp 203, the external electrode surface emission fluorescent lamp 203may further comprise auxiliary electrodes 202 a and 202 b, and may bemanufactured as an integrated type or a separated type. Moreover, it isclear that gas paths can be formed in the external electrode surfaceemission fluorescent lamp 203, as shown in FIG. 16, and the constructionof the getter housing 209 containing the getter 208 therein can beapplied to the backlight unit. These applications are included in thescope of the present invention.

A driving device usable for the above-described external electrodesurface emission fluorescent lamp having main electrodes and auxiliaryelectrodes will be described later. An embodiment of the externalelectrode surface emission fluorescent lamp having main and auxiliaryelectrodes is shown in FIG. 22.

FIG. 23 is a block diagram of a device for driving an external electrodesurface emission fluorescent lamp according to an embodiment of thepresent invention. Referring to FIG. 23, the driving device comprises amain controller 310, a priming circuit 320, and a lighting maintainingcircuit 330. The main controller 310 lights a surface emissionfluorescent lamp 350 in response to a control signal outputted from anLCD controller 360 which is a higher control unit. The priming circuit320 supplies power to auxiliary electrodes 305 so as to generate initialcharged particles in the external electrode surface emission fluorescentlamp 350 in response to a control signal outputted from the maincontroller 310. The lighting maintaining circuit 330 supplies power tothe main electrodes 303 so as to supply a lighting maintaining voltageusing the charged particles generated by the priming circuit 320.

The external electrode surface emission fluorescent lamp 350 isfundamentally the same as the surface emission fluorescent lamp 301 ofFIG. 22. For convenience of description, the surface emissionfluorescent lamp is designated by reference numeral 350 later. Further,it must be understood that external electrodes represent both the mainelectrodes 303 and the auxiliary electrodes 305, and are connected, asshown in FIG. 22.

The operations of the driving device having the above construction aredescribed in detail.

If a driving signal for initiating the operation of the driving deviceis received from the LCD controller 360 which is a higher controller,the main controller 310 outputs the driving signal to the primingcircuit 320, and turns off the priming circuit 320. In this case, beforecharged particles generated in the external electrode surface emissionfluorescent lamp 350 disappear, the main controller 310 applies adriving signal to the lighting maintaining circuit 330 and drives theexternal electrode surface emission fluorescent lamp 350 using thegenerated charged particles. Such a lit condition is maintained until anOFF control signal is inputted to the main controller 310 from the LCDcontroller 360.

FIG. 25 is a detailed circuit diagram of the driving device of thepresent invention. The main controller 310 comprises a timing controllerfor supplying power, to the auxiliary electrodes 305 for a predeterminedperiod of time in response to a control signal received from the LCDcontroller 360 to perform an initial lighting operation and thereaftersupplying lighting power to the main electrodes 303. Further, the maincontroller 310 comprises a pair of resistors R11 and R12 connected inseries with the priming circuit 320 and the lighting maintaining circuit330, respectively, so as to apply driving signals to the priming circuit320 and the lighting maintaining circuit 330.

Therefore, if a lighting signal is inputted from the LCD controller 360,the main controller 310 controls the timing to allow the priming circuit320 to generate charged particles in the external electrode surfaceemission fluorescent lamp 350 using power supplied through the auxiliaryelectrodes 305 from the priming circuit 320. Thereafter, before thegenerated charged particles disappear, the lighting maintaining circuit330 supplies power to the surface emission fluorescent lamp 350 throughthe main electrodes 303, thus operating the external electrode surfaceemission fluorescent lamp 350 at a low voltage. The predetermined periodof time for driving the priming circuit 320 is determined by a lightingmaintaining time of a fluorescent material required to generatesufficient number of charged particles in the surface emissionfluorescent lamp 350.

Further, the priming circuit 320 is comprised of a transformer T1 forself-excited driving, a resonance capacitor C22, a pair of switchingtransistors Q1 and Q2, a transistor Q3 for receiving a signal from themain controller 310 to drive the switching transistors Q1 and Q2,resistors R21 and R22 for controlling a voltage and a current inputtedto a gate, and a line filter consisting of a coil L21 and a capacitorC21 to stabilize an inputted current, thus enabling a voltage to beapplied to the auxiliary electrodes 305 of the external electrodesurface emission fluorescent lamp 350.

The lighting maintaining circuit 330 is used to receive a signal fromthe main controller 310 and apply a high voltage through the mainelectrodes 303 before charged particles formed in the external electrodesurface emission fluorescent lamp 350 by the priming circuit 320disappear. The lighting maintaining circuit 330 is comprised of atransformer T2 for self-excited driving, a resonance capacitor C32, apair of switching transistors Q3 and Q4, transistors Q5 and Q6 forreceiving a control signal from the main controller 310 to drive theswitching transistors Q3 and Q4, resistors R31 and R32 for controlling avoltage and a current inputted to a gate, and a line filter consistingof a coil L31 and a capacitor C31 to stabilize an inputted current, thusenabling a voltage to be applied to the main electrodes 303 of theexternal electrode surface emission fluorescent lamp 350.

Further, FIG. 24 is a block diagram showing another driving devicefurther comprising a feedback circuit 340 according to anotherembodiment of the present invention. The driving device comprises a maincontroller 310, a priming circuit 320, a lighting maintaining circuit330 and a feedback circuit 340. The main controller 310 lights a surfaceemission fluorescent lamp 350 in response to a control signal outputtedfrom the LCD controller 360, and outputs a control signal to control thebrightness of the external electrode surface emission fluorescent lamp350 to correspond to brightness set by a user. The priming circuit 320supplies power to the auxiliary electrodes 305 so as to generate initialcharged particles in the external electrode surface emission fluorescentlamp 350 in response to the control signal outputted from the maincontroller 310. The lighting maintaining circuit 330 supplies power tothe main electrodes 303 so as to apply a lighting maintaining voltageusing the charged particles generated by the priming circuit 320. Thefeedback circuit 340 detects a current flowing into the externalelectrode surface emission fluorescent lamp 350, converts the currentinto a voltage, and applies the voltage to the main controller 310 so asto control the brightness of the lamp 350 through the lightingmaintaining circuit 330. If the embodiment of FIG. 24 is compared withthat of FIG. 23, the driving device further comprises the feedbackcircuit 340, and further has a function of controlling the brightness ofthe external electrode surface emission fluorescent lamp 350 by the maincontroller 310 using a feedback operation of the feedback circuit 340.

That is, if power is supplied through the lighting maintaining circuit330, a current flowing into the external electrode surface emissionfluorescent lamp 350 is detected by the feedback circuit 340, thedetected current is converted into a voltage, and the, voltage isinputted to the main controller 310. Due to this voltage, the maincontroller 310 controls the brightness of the external electrode surfaceemission fluorescent lamp 350 by applying a PWM signal to the lightingmaintaining circuit 330. A setting value for brightness control isinputted to the LCD controller 360 by the user, and then inputted to themain controller 310 of the driving device, together with the drivingsignal of the LCD controller 360.

FIG. 26 is a detailed circuit diagram of the driving device of FIG. 24,wherein detailed descriptions are omitted because the circuitconstruction of FIG. 26 is similar to that of FIG. 25. The feedbackcircuit 340 is comprised of a rectifier consisting of a pair of diodesD41 and D42 to detect the current flowing into the external electrodesurface emission fluorescent lamp 350, a resistor R41 for converting thedetected current into a voltage, and a line filter consisting of acapacitor C41 and a resistor R42 to stably transmit the voltage inputtedfrom the resistor R41 to the main controller 310.

The operations of the device for driving the surface emissionfluorescent lamp for LCDs of the present invention having the aboveconstruction are described with reference to a flowchart of FIG. 27 asfollows.

First, if a user turns on a power lamp so as to operate a device onwhich an LCD panel is mounted, the LCD controller 360 applies a drivingsignal to the driving device at step S1. The driving signal from the LCDcontroller 360 is inputted to the main controller 310 of the drivingdevice. If the driving signal is inputted, the main controller 310outputs a driving signal to the priming circuit 320 at step S2. Thepriming circuit 320 is operated for a predetermined period of time setaccording to RC time constant. After the operation of the primingcircuit 320 is finished at step S3, the main controller 310 outputs adriving signal to the lighting maintaining circuit 330 to light theexternal electrode surface emission fluorescent lamp 350 at step S4.That is, after power is supplied to the auxiliary electrodes 305 of theexternal electrode surface emission fluorescent lamp 350 to generatecharged particles in the external electrode surface emission fluorescentlamp 350, power is supplied to the fluorescent lamp 350 through the mainelectrodes 303 using the lighting maintaining circuit 330 before thecharged particles disappear. If the feedback circuit 340 is not furtherincluded in the driving device, the above operations are repeatedlyperformed.

As described above, if power is supplied by the lighting maintainingcircuit 330, the external electrode surface emission fluorescent lamp350 maintains its lit condition, thereby providing light sources to theLCD screen. Such a lighting maintaining operation is repeatedlyperformed until an OFF control signal is inputted from the LCDcontroller 360.

Further, if the feedback circuit 340 is further included in the drivingdevice, as shown in FIG. 24, the main controller 310 controls thebrightness by comparing a value set by the user with a measured valueinputted by feedback using a voltage value inputted from the feedbackcircuit 340, and then outputting a voltage signal to the lightingmaintaining circuit 330 in a PWM manner at step S5. Such a brightnesscontrol operation is repeatedly performed until the OFF control signalis inputted from the LCD controller 360.

INDUSTRIAL APPLICABILITY

As described above, the present invention is advantageous in that it caneasily produce surface light sources with high brightness and highbrightness uniformity compared with a conventional edge-type backlightunit or a direct-type backlight unit using cold cathode fluorescentlamps, reduce a calorific value of an LCD panel due to electrodes of thefluorescent lamp, prevent breakdown of lamps due to breakdown ofelectrodes, and extend the lives of fluorescent lamps.

Further, the present invention is advantageous in that electrodes of asurface emission fluorescent lamp used for LCD backlighting areconstructed as external electrodes, thus simplifying a manufacturingprocess of surface emission fluorescent lamps, improving productivitythereof, easily producing a large-scale backlight unit, and enablingproduced LCDs to be miniaturized and thinned.

Further, the present invention is advantageous in that an initiallighting voltage for generating charged particles is applied to thesurface emission fluorescent lamp for LCDs having main electrodes andauxiliary electrodes, charged particles are generated, and a lightingmaintaining voltage is applied to the surface emission fluorescent lampbefore the generated charged particles disappear, thus maintaining thelit condition of the surface emission fluorescent lamp, stably operatingthe surface-emission fluorescent lamp even at a low voltage, andreducing continuous stress of a transformer and loss of switchingdevices due to a high voltage for initial lighting.

1. An LCD backlight unit, comprising: an inverter for generating first and second alternating current (AC) voltages using a direct current (DC) voltage and supplying the first and second AC voltages through first and second output lines, respectively; a plurality of external electrode fluorescent lamps comprised of odd-numbered external electrode fluorescent lamps each having a first end electrode connected to the first output line of the inverter, and even-numbered external electrode fluorescent lamps each having a first end electrode connected to the second output line of the inverter, wherein second end electrodes of the odd-numbered and even-numbered external electrode fluorescent lamps, which are not connected to the first and second output lines, are grounded; and a base for allowing the plural external electrode fluorescent lamps to be fixed, wherein the inverter comprises: a line filter for rectifying a DC voltage supplied through a DC power unit and outputting the rectified DC voltage; a pulse generator for generating switching driving pulses; a pair of driving buffers for selectively outputting the driving pulses generated by the pulse generator; a pair of resonance circuits driven by the driving pulses outputted from the driving buffers to respectively converter the DC voltage received from the line filter into an AC voltage and output the AC voltage; and a pair of step-up transformers for respectively amplifying AC voltages outputted from the resonance circuits and outputting the amplified AC voltages to the external electrode fluorescent lamps which are divided into two groups, and wherein the base for allowing the external electrode fluorescent lamps to be fixed comprises: a pair of isolating plates longitudinally extended and arranged opposite to each other; and a pair of lamp fixing plates having both ends connected to the isolating plates, and having a plurality of lamp fixing holes oppositely formed at regular intervals.
 2. The LCD backlight unit according to claim 1, wherein the first and second output lines are arranged such that they alternately enclose the external electrode fluorescent lamps to intersect at sides of the external electrode fluorescent lamps, and to be opposite to each other at top and bottom portions thereof.
 3. The LCD backlight unit according to claim 1, wherein the first and second AC voltages supplied through the first and second output lines from the inverter have the same phases and same frequencies.
 4. The LCD backlight unit according to claim 1, wherein the inverter further comprises a feedback circuit for detecting secondary currents of the external electrode fluorescent lamps and applying a signal for brightness control to the pulse generator so as to control brightness of the external electrode fluorescent lamps. 